The present invention relates to a tread for propulsion in snow, and particularly to a tread for a power-driven ski type of device, which may be a power-driven toboggan, ski-bob, snowmobile or other light, snow going vehicle. Throughout the text I will discuss the cleat as it applies to a power-driven ski, with the understanding that similar considerations hold true in the case of other devices of this type.
Power-driven ski and ski-bob are newcomers to the small family of motorized winter sports devices, and have been described in detail in my U.S. Pat. No. 3,853,192, issued on Dec. 10, 1974, and in my U.S. Patent Application Ser. No. 754,457 filed on Jan. 6, 1977, respectively, both of which are herein incorporated by reference.
Basically, the ski is propelled by a tread which circulates around the posterior ski portion at a linear pitch-line speed which is approximately equal to the ski's ground speed, which may exceed 30 m.p.h.. The tread is circulateably supported by sprockets which are preferably small in order to keep the ski's profile compact and for other reasons discussed in my above mentioned patent. Consequently, the tread swings around the sprocket at high angular speeds, and the portions of the tread that protrude outwardly from the tread's pitch-line experience sharp inertial forces due to acceleration and deceleration of the cleat upon starting and ending, respectively, their travel over the sprocket, in addition to the centrifugal forces.
Operating a mechanical device with moving parts in snow environment poses some unique problems. Snow may readily transfer from fluffy powder to water or to hard ice, depending on the temperature and mechanical conditions it is subjected to. When the tread circulates over the sprockets it tends to accept a build up of snow which is packed, centrifugally and mechanically, between the cleats and the sprocket, until it interferes with the proper engagement between the two, often causing early mechanical failure of the tread, and in many instances of the ski posterior body portion. Therefore, it seems essential to prevent such build up of snow by preventing the entrapment of snow between the cleats and the sprockets.
Some of the objects of the present invention are to provide a propulsion cleat for the power-driven ski's tread that would withstand the inherent mechanical punishment, by being strong and flexible simultaneously, while at the same time effectively providing a forward thrust to the ski. A further object is to minimize the cleat's weight so as to minimize the centrifugal and inertial forces previously mentioned.